<template>
  <scroll class="listview" 
          :data="data" ref="listview" 
          :listenScroll = "listenScroll"
          :probeType="probeType"
          @scroll="scroll"
  >
      <ul>
          <li v-for="group in data" class="list-group" ref="listGroup">
              <h2 class="list-group-title">{{group.title}}</h2>
              <ul>
                  <li @click="selectItem(item)" v-for="item in group.items" class="list-group-item">
                      <img class="avatar" v-lazy="item.avatar"/>
                      <span class="name">{{item.name}}</span>
                  </li>
              </ul>
          </li>
      </ul>
      <div class="list-shortcut" @touchstart="onShortcutTouchStart" @touchmove.stop.prevent="onShortcutTouchMove">
          <ul>
              <li v-for="(item, index) in shortcutList" class="item" :class="{'current': currentIndex===index}" :data-index="index">
                  {{item}}
              </li>
          </ul>
    </div>
          <div class="list-fixed" ref="fixed" v-show="fixedTitle">
              <h1 class="fixed-title">{{fixedTitle}}</h1>
          </div>
          <div v-show="!data.length" class="loading-container">
              <loading></loading>
          </div>
  </scroll>
</template>

<script type="text/ecmascript-6">
import Scroll from "base/scroll/scroll";
import { getData } from "common/js/dom";
import Loading from "base/loading/loading"

const ANCHOR_HEIGHT = 18
const TITLE_HEIGHT =30

export default {
    created() {
      this.touch = {}
      this.listenScroll = true
      this.listHeight = []
      this.probeType = 3
    },
    data() {
        return {
            scrollY: -1,
            currentIndex: 0,
            diff: -1
        }
    },
  props: {
    data: {
      type: Array,
      default: []
    }
  },
  computed: {
    shortcutList() {
      return this.data.map(group => {
        return group.title.substr(0, 1);
      });
    },
    fixedTitle() {
        if (this.scrollY > 0) {
            return ''
        }
        return this.data[this.currentIndex]? this.data[this.currentIndex].title: ''
    }
  },
  methods: {
      selectItem(item) {
          this.$emit('select', item)
      },
    onShortcutTouchStart(e) {
      let anchorIndex = getData(e.target, "index");
      let firstTouch = e.touches[0]
      this.touch.y1 = firstTouch.pageY
      this.touch.anchorIndex = anchorIndex
      this._scrollTo(anchorIndex)
    },
     onShortcutTouchMove(e) {
        let firstTouch = e.touches[0]
        this.touch.y2 = firstTouch.pageY
        let delta = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0
        let anchorIndex = parseInt(this.touch.anchorIndex) + delta  
        this._scrollTo(anchorIndex)
      },
      refresh() {
          this.$refs.listview.refresh()
      },
      scroll(pos) {
          this.scrollY = pos.y
      },
      _scrollTo(index) {
        if(!index && index !== 0){
              return
          }
          if(index < 0) {
              index = 0
          }else if (index > this.listHeight - 2) {
              index =this.listHeight.length - 2
          }
          this.scrollY = -this.listHeight[index]
        this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0);
      },
      _calculateHeight() {
        this.listHeight = []
        const list = this.$refs.listGroup
        let height = 0
        this.listHeight.push(height)
        for (let i = 0; i < list.length; i++) {
          height += list[i].clientHeight
          this.listHeight.push(height)
        }
      }
  }, 
  watch: {
      data() {
          setTimeout(() => {
              this._calculateHeight()
          }, 20)
      },
      scrollY(newY) {
          const listHeight = this.listHeight

            if(newY >0 ){
            this.currentIndex = 0
            return
            }
          for (let i = 0; i < listHeight.length; i++) {
            let height1 = listHeight[i]
            let height2 = listHeight[i + 1]
            if (-newY >= height1 && -newY < height2) {
                this.currentIndex = i
                this.diff = height2 + newY
                  return
              }
          }
          this.currentIndex = listHeight.length - 2
      },
      diff(newVal) {
          let fixedTop = (newVal > 0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT :0
          if(this.fixedTop === fixedTop) {
              return
          }
          this.fixedTop = fixedTop
          this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`
      }
  },
  components: {
    Scroll,
    Loading
  }
};
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
@import '~common/stylus/variable';

.listview {
    position: relative;
    width: 100%;
    height: 100%;
    overflow: hidden;
    background: $color-background;

    .list-group {
        padding-bottom: 30px;

        .list-group-title {
            height: 30px;
            line-height: 30px;
            padding-left: 20px;
            font-size: $font-size-small;
            color: $color-text-l;
            background: $color-highlight-background;
        }

        .list-group-item {
            display: flex;
            align-items: center;
            padding: 20px 0 0 30px;

            .avatar {
                width: 50px;
                height: 50px;
                border-radius: 50%;
            }

            .name {
                margin-left: 20px;
                color: $color-text-l;
                font-size: $font-size-medium;
            }
        }
    }

    .list-shortcut {
        position: absolute;
        z-index: 30;
        right: 0;
        top: 50%;
        transform: translateY(-50%);
        width: 20px;
        padding: 20px 0;
        border-radius: 10px;
        text-align: center;
        background: $color-background-d;
        font-family: Helvetica;

        .item {
            padding: 3px;
            line-height: 1;
            color: $color-text-l;
            font-size: $font-size-small;

            &.current {
                color: $color-theme;
            }
        }
    }

    .list-fixed {
        position: absolute;
        top: 0;
        left: 0;
        width: 100%;

        .fixed-title {
            height: 30px;
            line-height: 30px;
            padding-left: 20px;
            font-size: $font-size-small;
            color: $color-text-l;
            background: $color-highlight-background;
        }
    }

    .loading-container {
        position: absolute;
        width: 100%;
        top: 50%;
        transform: translateY(-50%);
    }
}
</style>